Observing Campaign to Monitor Magnetically-Active Dwarfs for Long-Term Variability
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| The Sun in soft X-rays obtained by the Yohkoh satellite, February 1, 1992 (Courtesy: Yohkoh/Montana State University) | |
From AAVSO Alert Notice 406:
The observers of the AAVSO are asked to participate in a long-term
photometric monitoring campaign on a number of magnetically active dwarf
stars, requested by Dr. Styliani (Stella) Kafka of the Department of
Terrestrial Magnetism, Carnegie Institute of Washington. She
requests long-term monitoring of these targets with an observing
frequency of one observation every three days taken with one or more
filters. When multiple filters are available, the preferred observations
are (in order of precedence): Rc, V, Ic, and B. Please observe such
that you obtain a signal to noise of at least 50 (100 or higher is
preferred).
These objects are all nearby dwarfs known or suspected to have magnetic
activity, primarily of the UV Ceti (flare star) or BY Draconis subtypes.
Long-term photometric monitoring of these objects will be used in
conjunction with other multiwavelength observations from ground-based
facilities including the Magellan 6.5-meter and DuPont 2.5-meter
telescopes in Chile to understand the long-term magnetic activity cycles
of these stars. Such a study can reveal information about the physical
natures of these stars, but also about their near space environments and
habitability for life.
These objects are red, and the variability amplitudes are low, often
well below 0.1 magnitudes. The long-term variability due to stellar
activity cycles may be much lower. Photometric accuracy rather than the
number of observations are key to the success of this project.
Unaccounted-for atmospheric effects such as extinction will likely
overwhelm any long-term signal from these stars. Observers are strongly
urged to fully calibrate their systems and to carefully reduce and
transform their photometry to standard photometric passbands, including
corrections for airmass/atmospheric extinction.
Because of the long-term nature of this project, observers are asked to
select one or more targets from the list below that are best suited to
their system, and to add them to their observing schedules at a low
priority. One observation every few days will be sufficient to trace the
long-term behavior. Intensive time-series is not required, although
observers may detect rapid, large-amplitude variations occurring in the
flare stars; if you believe a flare is occurring during your exposure,
please indicate this in the comments field when submitting data. Note
that flares will have much larger amplitude at bluer wavelengths.
Please also note that the majority of these stars are high proper motion
systems. Charts generated with AAVSO VSP may not accurately reflect the
current positions of these objects. If you perform automated aperture
photometry of your exposures, please verify that the object is in the
expected position. We also request that you save your reduced frames
for future analysis. We may request that you submit your frames to the
AAVSO website or directly to Dr. Kafka at some point.
Please contact Matthew Templeton (matthewt at aavso.org) for AAVSO- or
other observing-related questions, and Stella Kafka (email at email.edu)
for specific, project-related questions.
AAVSO participation in this project is important and your help will be
greatly appreciated!
Observing Schedule
This is a very long-term campaign, with low-level but consistent observations
requested over two years or more. Intensive time-series are not required.
We suggest that you select a small number of stars per season and concentrate
on only those. A large number of observers individually making a small number
of well-calibrated observations would easily fulfil the needs of this program.
Select stars for a given observing quarter such that the target is at its
highest elevation when performing photometry, preferably as close to transit
as possible, to minimize extinction effects.
Photometric requirements
Calibration and extinction-correction of photometry is strongly encouraged;
doing so enables us to combine data from multiple observers, and to eliminate
spurious sources of variability like airmass effects. This is primarily an
instrumental campaign in which calibrated observations taken in standard
Johnson-Cousins filters are preferred. Filters requested in order of
preference are: Cousins Rc, Johnson V, Cousins Ic, and
Johnson B; other filters such as Sloan may be used if they are
available. Note that because these targets are red stars, they will likely
be brighter in Rc,Ic than in V, and much brighter than
in B.
For a basic guide to system calibration and photometry, see the current
version of the
CCD Observing Manual. This manual is currently under revision, but will
provide a basic overview of how to calibrate your system and apply this
information to your photometry. For questions, please contact Arne Henden
(arne at aavso.org), Matthew Templeton (matthewt at aavso.org), or post
a question to the
AAVSO-Photometry Mailing List. There will also be a one-hour presentation
on calibration and transformation of photometry by Dr. Arne Henden at the
AAVSO Annual
Meeting on November 5-7, 2009. Attendees of the meeting are encouraged to
attend this important lecture.
Target List
Observations of the following stars are requested as part of this campaign:
